Bone grafts are used worldwide to treat musculoskeletal defects in millions of orthopaedic, neurocranial, plastic, and oral/dental surgeries each year [1]. The gold standard bone graft material is autograft bone. However, besides limited supply, prolonged surgery time and increased blood loss, autograft bone harvest is associated with many donor site morbidities including pain, gait disturbance, thigh paresthesia for iliac crest donor sites, and infection, neurologic deficits, and hematomas for calvarial donor sites. In addition, aging and osteoporosis reduce stem cell availability and activity in the bone marrow, creating an unfavorable microenvironment that promotes adipogenesis over osteogenesis [2], [3], which may account for failed fracture healing in up to 50% of osteoporotic patients [4]. Thus, for patients with poor quality bone, iliac bone harvest can lead to severe complications such as iliac crest fracture and complete pelvic ring failure [5]. On top of this, any bone harvested from osteoporotic patients can contain the same suboptimal microenvironment and diminished repair capacity [6]. Overall, autograft bone use is complicated by limited supply, significant harvest morbidities, and inconsistent bone regeneration properties.
Current autologous bone graft substitutes have undesirable side effects or lower efficacy. The most effective bone graft substitute in use is BMP2 (INFUSE® Bone Graft) [7]. BMP2, however, has elicited life-threatening cervical swelling [8], osteoclast activation [9], adipogenic differentiation [2], bone cyst formation [10,11], and tumor growth [12]. Newer combinations of cryopreserved allogeneic mesenchymal stem cells and allograft cancellous bone [e.g. Osteocel®, Trinity® Evolution™ (TE®)] involve processing steps that remove immunogenic components but also deplete osteogenic cells and osteoinductive factors—making these products less effective (unpublished data). Thus, there is an urgent need for safer and more effective bone graft substitutes that retain high efficacy even in suboptimal micro environments.
While many current bone graft substitutes promote various degrees of osteogenesis, few provide adequate numbers of the appropriate stem cells, and none provide factors that concomitantly promote osteogenesis while inhibiting adipogenesis [13].
Stem cells can accelerate bone regeneration by promoting osteoprogenitors and improve vascular ingrowth [14]. Current conventional stem cell sources, however, have significant drawbacks. Low stem cell numbers/high donor site morbidity limit the use of fresh autologous bone marrow [15,16], while the need for culture and long derivation times hamper the use of bone marrow stem cells (BMSC) or adipose derived stem cells (ASC). Culturing also introduces immunogenicity, infection, and genetic instability/potential tumorigenicity risks [17,18]. In addition, significant cell heterogeneity, including high numbers of non stem cells, non viable cells, and the presence of differentiation inhibiting endothelial cells [19,20] may decrease the osteogenic efficacy of adipose total stromal vascular fractions.
The embodiments described below address the above identified problems and needs.